This invention relates to the field of manually operated, hand held, liquid dispenser pumps and, more particularly, to pumps having plungers which may be locked to prevent the inadvertent discharge or leakage of the product.
A variety of structures have been employed as a means for locking down the plunger of a hand held, liquid dispenser pump during periods of non-use. One such locking means is the use of a threaded engagement between the plunger and the container cap. A problem with this type of locking engagement, however, is that the unthreading of the plunger often leads to loosening of the cap from the container. Another structure used as a locking means is a protective overcap. Although the cap immobilizes plunger reciprocation during periods of non-use, the cap represents a supplemental accessory which is often misplaced. A third structure used as a locking means are locking tongues or fingers which are deflectable into the path of reciprocation. Reliance on the elastic memory of the tongues or fingers for retracting them away from the path of reciprocation to permit actuation of the pump may eventually render the pump inoperable if the elastic memory is lost or diminishes during the shelf life of the product.
All of these various approaches for immobilizing the plunger are either unreliable, somewhat cumbersome, or complicated and therefore expensive.